Conventionally, the use of e-mail has been popularized as means of communication through a communication network. An e-mail is written with a terminal (for example, a personal computer) by a sender and then transmitted by communication means such as a telephone line to a company (provider) which provides access to the Internet for the sender with his mail account. The internet provider serves to temporarily stores the mail in an e-mail server and then transfer it through the Internet to the internet provider which has issued the mail account of the addressee. Since the mail as transferred is stored in the e-mail server of the internet provider of the addressee, the mail can be received by the addressee with a terminal (for example, a personal computer) when he make connection of the terminal with the internet provider through communication means such as a telephone line and send a request for transmission of the mail in response to which the internet provider transmits the mail stored in the e-mail server to the terminal of the addressee through communication means such as a telephone line.
However, it has been recognized that there are following problems in the case of the existing e-mail systems.
Since the current situation of the delivery of the e-mail depends on the settings of the respective transmission and relay point servers, it is not certain that the e-mail as transmitted by a sender is quickly passed through the Internet and immediately received by the addressee server.
Also, the sender server does not guarantee delivery of a mail, and it is not certain that the addressee server transmits an notification of completion of the operation which is received by the sender server, and therefore the sender of the mail can not know very important information relating to communication, i.e., “when the mail was delivered to the addressee” and “when the addressee read the mail”.
Furthermore, it is also not certain that the sender can confirm the fact of if the transmission fails, and therefore the sender can not certainly know a very important problem relating to information delivery, i.e., “the mail as transmitted has not been received by the addressee”.
Furthermore, since no encryption mechanism is implemented in the communication protocols, SMTP (Simple Mail Transfer Protocol) and POP (Post office Protocol), the mail is usually exchanged in terms of plane texts. Because of this, the confidentiality of e-mail is not sufficiently secured so that it is difficult to use a mail for important correspondence, messages which require high confidentiality and so forth.
Furthermore, since typical e-mail browsing software (mail client software) downloads the mail contents from an e-mail server, it is necessary to set up mail software for each mail terminal and for each mail account so that the setup procedure is troublesome for such a user as makes use of a plurality of terminals or a plurality of mail accounts. Furthermore, in the case of the above software, the setup is made in order that a mail is deleted from the server after downloading the same so that once a mail is read with one terminal, the mail can not be read with any other terminal and therefore mails are scattered about the respective terminals. For this reason, information carried by the e-mail is scattered to impede effective communication.